Process control systems, like those used in chemical, petroleum, pharmaceutical, pulp and paper, or other manufacturing processes, typically include one or more process controllers communicatively coupled to at least one host including at least one operator workstation and to one or more field devices configured to communicate via analog, digital or combined analog/digital communication protocols. The field devices, which may be, for example, device controllers, valves, valve actuators, valve positioners, switches and transmitters (e.g., temperature, pressure, flow rate, and chemical composition sensors) or combinations thereof, perform functions within the process control system such as opening or closing valves and measuring or inferring process parameters. A process controller receives signals indicative of process measurements made by the field devices and/or other information pertaining to the field devices, uses this information to implement a control routine, and generates control signals that are sent over buses or other communication lines to the field devices to control the operation of the process.
A typical process control system is segmented into one or more control loops that are operated by a process controller. Each control loop includes a number of inputs from one or more field devices, a control algorithm, and one or more outputs. Each of these field devices is typically coupled to the process controller via one or more I/O cards and a respective communication path (e.g., a two-wire cable, a wireless link, or an optical fiber). The I/O cards receive inputs from the field devices and forward the inputs to the process controller. Likewise, the output signals are transmitted to field devices within the process control system via the I/O cards. The quality of any particular control loop is determined by the ability of the control loop to read an input change in a timely manner, perform necessary control calculations, and generate a response in the form of an output signal. In some cases, a communication path may delay an input signal from being received in a timely manner by a process controller, thereby degrading the quality of any control loop that uses that communication path.